Recently, more and more fiber are recycled and reused in paper making processes. In addition, more attention is being paid to the sustainable development of natural environment, forest resources protection and energy resources conservation. Recycled fiber is also called secondary fiber, which is respective to the primary fiber or raw fiber that originates directly from wood resources. Recycled fiber originates from used waste paper, for example, old newspaper, magazine, corrugated paper, paperboard, and the like. After thorough processing steps such as pulping, screening, purifying, stripping, washing, concentrating (or thickening), heat dispensing, rubbing, floating, refining and bleaching, etc., the recycled fiber and lignin therein are reused in papermaking processes.
Using recycled fiber to produce paper or paperboard, etc., in the papermaking industry, can significantly reduce wood cutting and energy consumption, save water resources, and the utilization efficiency of fiber may become more effective (see Reference 1: Environmental Paper Network. Green Press Initiative. 2007. Retrieved 23 Oct. 2011). In Europe, waste paper occupies more than 60% of the whole papermaking fiber raw materials (see Reference 2: European declaration on paper recycling 2006-2010. Monitoring Report 2007. European recovered paper council. Retrieved 17 Jan. 2009). In several papermaking plants in China, such proportion is more than 70%. Since there are also a number additives, such as dry strength agents, starch, and fillers, in recycled fiber, reusing a large amount of additives adsorbed in recycled fiber along with the reutilization of recycled fiber is desired. Providing for the reuse of additives reduces the amount of the additives added in the later papermaking procedure, improves the efficiency of the utilization of recycled fiber, and achieves economic and sustainable developments.
However, in processes utilizing recycled fiber to produce paper and paperboard, during a pulping procedure the recycled fiber is broken or the lengths of fiber are shortened, and the additives adsorbed in the recycled fiber are destroyed or degraded resulting in fiber quality that does not meet the quality requirements of making some kind of paper. Therefore, the amount of fiber or additives has to be increased so as to fulfill the requirements of the product quality. For example, after recycled waste paper is pulped, a large amount of additives such as dry strength agents or starch has to be added to produce paper with satisfied strength. Thus, preserving the additives adsorbed in recycled fiber from destruction and degradation is an important means for improving the utilization efficiency of recycled fiber. It can reduce costs and increase the quality of paper products.
At present, reutilization of the additives in recycled fiber has not been paid high attention, which leads to the decline of reusing efficiency.